The present invention relates to a cleaning device by which the surface of the image carrier of an electrostatic copier is cleaned.
In general, a toner image formed on the surface of the image carrier of the electrostatic recording apparatus is not completely transferred onto a recording sheet, and residual toner that has not been transferred is left on the surface of the image carrier. In order to accomplish the successive copying operation, it is necessary to remove this residual toner from the surface of the image carrier for cleaning. In order to achieve the object, there is provided a cleaning device by which the residual toner is scraped off with a blade. In this cleaning device, an end of the blade comes into contact with the image carrier, and the cleaning device is classified into two types, one is a trail system and the other is a counter system. In the trail system, an end of the blade is contacted with the image carrier being set in a downstream direction of the image carrier. In the counter system, the end of the blade is contacted with the image carrier being set in an upstream direction of the image carrier. Since the end of the blade is set in the upstream direction of the image carrier in the counter system, the toner cleaning property of the counter system is superior to that of the trail system.
In this connection, durability of the cleaning device can be improved when the blade is contacted with the image carrier only in the process of cleaning and the blade is separated from the image carrier after the completion of cleaning.
In the color image apparatus, developers of a plurality of colors are used, and processes of charge, exposure and development are repeated so that a color toner image of 3 or 4 colors is formed on the image carrier, and then the formed color toner image is transferred onto a recording sheet at one operation. In this color toner image forming apparatus, the cleaning blade is separated from the image carrier while the color toner image is being formed on the image carrier, and after the completion of transfer of the color toner image, the blade is contacted with the image carrier and residual toner on the image carrier is scraped off for cleaning.
However, in the cleaning device described above in which the blade is used for removing residual toner, the following problems may be encountered and the formed images are stained with residual toner.
In the counter system in which the contact and release means for contacting and releasing an end of the blade is provided, only when the residual toner is removed from the image carrier, the end of the blade comes into contact with the image carrier, and after the completion of cleaning, the blade is separated from the image carrier. In this case, the blade is contacted with the image carrier which is being rotated. At this time of contact of the blade with the image carrier, the blade bounces up.
In the color image apparatus, developers of a plurality of colors are used, and processes of charge, exposure and development are repeated so that a color toner image is formed on the image carrier, and then the formed color toner image is transferred onto a recording sheet at one operation. In this color toner image forming apparatus, the blade frequently bounces up when the blade end is contacted with and released from the image carrier.
When the blade bounces like this, the surface of the image carrier is damaged and sometimes stained by the marks of bounce. The damage and stain may affect the formation of an image on the image carrier, and it is difficult to provide an image of high quality.
When the blade coming into contact with the image carrier is released, residual toner on the blade and image carrier is scattered and deposited on an image formed on the image carrier, so that the formed image becomes defective. In this way, a problem of the spill of toner occurs.
Sometimes, this problem of the spill of toner spreads to a position about 160 mm distant from the blade release position. In order to solve above problem, a surplus portion is provided on the conventional image carrier irrespective of the formation of a toner image, and the scattered toner is deposited on this surplus portion.
However, when this surplus portion is provided on the image carrier, dimensions of the image carrier are increased, and the image carrier occupies a large space in the image forming apparatus, so that it is difficult to downsize the color image forming apparatus. Since the dimensions of the image carrier are increased, it is necessary to raise the moving speed of the image carrier. Accordingly, more precise mechanisms are required for controlling the speed, and the manufacturing cost is increased.
In the case of a cleaning device in which the contact and release of the cleaning means are repeatedly conducted, residual toner is scraped and scattered from the image carrier as illustrated in the schematic illustration of FIG. 10(a). Then, as illustrated in the schematic illustration of FIG. 10(b), the scattered toner tends to be deposited on a contact surface of the cleaning blade on the downstream side. As a result, the blade surface is gradually stained by the deposited toner.
After the blade has been contacted with the image carrier, the residual toner on the image carrier is removed by the blade. At this time, the latent image still remains on the image carrier and passes through the blade. Therefore, as illustrated in the schematic illustration of FIG. 10(c), the toner deposited on the blade surface tends to scatter onto the residual latent image, especially the toner deposited on the blade surface opposed to the image carrier tends to scatter to an edge of the latent image, and the remaining latent image on the image carrier is developed by the scattered toner. In other words, what is called "blade development" is caused.
Conventionally, in order to prevent the occurrence of the blade development, the latent image is discharged by an AC discharger arranged before the blade. According to this AC discharging system, the cost of the apparatus including the electric power supply unit is very high, and further the durability of the wire used for a discharge electrode of corona discharge is low. The above problems may be encountered in the prior art.